The metal contamination of semiconductor wafers negatively affects the device characteristics of products. Examples of steps that cause metal contamination are various heat treatments in the process of manufacturing wafers, such as oxidation, diffusion, and epitaxial growth. For example, when a heavy metal such as Fe or Ni is contaminated into a silicon wafer by a heat treatment, a deep level is created in the band gap, functioning as a carrier trapping center or recombination center and causing p-n junction leaks in the device and decreasing its lifetime. Accordingly, providing a high-quality semiconductor wafer with little metal contamination requires a highly reliable method of evaluating the metal contamination in a semiconductor wafer following a heat treatment.
In this regard, Japanese Unexamined Patent Publication (KOKAI) No. 2009-302337, which is expressly incorporated herein by reference in its entirety, proposes managing the heat treatment processes in the process of manufacturing a semiconductor wafer by using a monitor wafer for monitoring contamination in heat treatment processes.
The metal contamination that is caused by heat treatment processes is roughly divided into contamination caused by metal impurities that contaminate from the heat treatment atmosphere and contamination in the form of diffusion in the vicinity of contact portions during heat treatment by metal impurities that adhere to the semiconductor wafer due to contact with a contamination source (such as particles containing metal components; wafer holders such as heat treatment boats, susceptors, and three-point support pins; and various metal manufacturing jigs) prior to and during heat treatment processes. The latter form of metal contamination occurs in localized fashion in the vicinity of contact portions.
Japanese Unexamined Patent Publication (KOKAI) No. 2009-302337 determines the presence or absence of metal contamination from the heat treatment atmosphere based on the level of a lifetime measurement value. However, it is difficult to evaluate the latter localized metal contamination by this method.